.task{
    display: none;
    position: fixed;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    background-color: rgba(0, 0, 0, .3);
}
.task .cont{
    width: 400px;
    height: 300px;
    background: #fff;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%,-50%);
    padding: 20px;
}